JosephHooker:
It is often said that all the conditions for the first production of a living organism are now
present,whichcouldeverhavebeenpresent.—Butif(andohwhatabigif)wecouldconceive
in some warm little pond with all sorts of ammonia and phosphoric salts,—light, heat,
electricityetc.present,thataproteincompoundwaschemicallyformed,readytoundergostill
more complex changes, at the present day such matter would be instantly devoured, or
absorbed,whichwouldnothavebeenthecasebeforelivingcreatureswereformed.
Thus,Darwinconcludedthatlifeisunlikelytooriginatetodaybecause
organismsarecontinuallyeatingthechemicalcompoundsthatareneeded.On
theotherhand,beforelifeexisted,chemicalconditionsfortheoriginoflife
wouldhavebeenprevalent.
Inthe1920s,theRussianbiochemistAlexanderOparinandtheBritishbiologist
J.B.S.Haldanebothrecognizedthattheenvironmentunderwhichlifearose
wouldhavelackedoxygen.Earth’soxygen-richatmosphereisaproductof
photosynthesisbyplants,algae,andbacteria.Anoxygen-freeatmospherewould
havebeenbettersuitedtoprebioticchemistrybecauseoxygenconvertsorganic
matterintocarbondioxide,whichpreventsthebuild-upofcomplexmolecules.
Indeed,acontemporarygeologist,AlexanderMacGregor,reportedin1927that
hehadfoundsedimentaryrocksdatingfromwithintheArchaeanAeon(3.8–2.5
Ga)thatshowedthattheancientatmospherelackedoxygen.Inparticular,
MacGregorobservedthatironmineralsinwhatisnowZimbabwewere
unoxidized,unliketherust-colouredironoxidesinmodernsedimentsthatare
producedwhenatmosphericoxygenreactswithiron-containingminerals.Today,
MacGregor’sdeductionissupportedbymanyotherdata(Chapter4).
OparinandHaldanealsoproposedthatgasesinEarth’searlyatmospherewould
havebeenconvertedbyultravioletsunlightorlightningintoorganicmolecules.
Inthe1950s,suchideasweretestedwhenStanleyMiller,astudentoftheNobel
Prize-winningchemistHaroldUrey,devisedanexperimentattheUniversityof
Chicago.Ablendofammonia,methane,hydrogen,andwatervapourwasputin
aflaskandelectricsparkspassedthroughthegastosimulatelightning.Miller
foundthatyellowishwatercondensedoutatthebottomoftheflask.Thisdark
residuecontainedorganicmolecules,includingvariousaminoacids—the
buildingblocksofproteins.Atthetime,theMiller–Ureyexperimentwas
trumpetedinthemediaasvirtuallysolvingtheproblemoftheoriginoflife.Life
wassaidtostartina‘primordialsoup’generatedbyatmosphericchemistry.In
1953,whenMillerwroteuphisresults,acommonview(datingbacktoOparin